Plaque fluids obtained from monkeys before and after application of sucrose have been analysed for their volatile metabolic products using high resolution capillary column and a gas chromatograph. A variety of volatile fatty acids was demonstrated in the plaque fluid samples and a decrase in the proportions of acetic and propionic to butyric acids was demonstrated following application of sucrose seen. Plaque fluid samples obtained fom irradiated and control monkeys have been analysed for L (+) and D (-) lactic acid. Following sucrose application, there was an expected sharp rise in the amount of the L (+) lactate. High concentrations of the D (-) form was found in all of the samples. Methane formation has been demonstrated in dental plaque and the reduction of proline to delta amino valeric acid (DAVA) determined. A pure culture of one of the organisms responsible for DAVA formation has been isolated.